This invention relates to a method of treating a hydrocarbon well with well treatment chemicals, in particular by down-hole placement of polymeric particles carrying well treatment chemicals or precursors or generators thereof, and to such particles and compositions and structures containing them.
During the operation of a hydrocarbon well (i.e. a gas or oil well) various down-hole problems arise such as corrosion of metal fittings, hydrocarbon flow-inhibiting deposition (e.g. of scale, gas clathrates, metal sulphides, waxes, gel polymers, microbial debris, etc.), generation of toxic hydrogen sulphide by sulphate-reducing bacteria, increased water flow into the producer bore, etc.
Thus, for example, where sea water is injected through an injection bore hole into an oil-bearing stratum to drive oil through the formation (i.e. the rock) into the producer well hole, differences in solutes in the injection water and the water already present in the formation can cause metal salts to precipitate as scale so causing gradually increasing clogging of the producer well hole.
Typically this is dealt with by applying a “squeeze” of scale inhibitor chemicals, i.e. chemicals which break down the scale and increase oil or gas flow. This generally involves ceasing hydrocarbon flow, forcing an aqueous solution of the scale inhibitor down the producer bore under pressure to drive the inhibitor solution into the formation, and restarting production. Such treatment generally allows a further six or so months of hydrocarbon flow before a further squeeze is required and each squeeze causes some damage to the formation surrounding the producer bore hole and as a result an increased flow of formation fragments (i.e. rock grains etc.) into the bore.
The producer bore hole in an oil well is generally lined in the hydrocarbon bearing stratum with “gravel packs”, sand containing filter elements, which serve to trap formation fragments and it has been proposed to include in such gravel packs ceramic particles coated with or impregnated with well treatment chemicals such as scale inhibitors (see EP-A-656459 and WO 96/27070) or bacteria (see WO 99/36667). Likewise treatment of the formation surrounding the producer well bore hole with well treatment chemicals before hydrocarbon production begins has also been proposed, e.g. in GB-A-2290096 and WO 99/54592.
Various polymeric, oligomeric, inorganic and other particulate carriers for well treatment chemicals are also known, e.g. ion exchange resin particles (see U.S. Pat. No. 4,787,455), acrylamide polymer particles (see EP-A-193369), gelatin capsules (see U.S. Pat. No. 3,676,363), oligomeric matrices and capsules (see U.S. Pat. Nos. 4,986,353 and 4,986,354), ceramic particles (see WO 99/54592, WO 96/27070 and EP-A-656459), and particles of the well treatment chemical itself (see WO 97/45625).
Particles coated or impregnated with or encapsulating a well treatment chemical however have the inherent problem that release of the well treatment chemical will take place relatively rapidly once the particles encounter water down-hole. Accordingly the protection they provide is relatively short lived.
There is thus a continuing need for well treatments which provide prolonged protection.